At many geothermal sources in current use, steam in the geothermal fluid exiting production wells is separated from brine, and expanded in a steam turbine for producing power and electricity. Often, the brine is simply discarded because it contains a relatively small amount of heat. However, the relative amounts of steam and brine produced at a given location will depend on the temperature at which the separation is carried out.
Recently, heat present in the brine has been utilized for producing power by employing a binary cycle in which, for example, steam in the geothermal fluid is used in a steam turbine, and the exhaust steam and brine in the geothermal fluid are used to supply heat to vaporize an organic fluid that is expanded in a vapor turbine for generating power. Also, often heat in the brine has been used merely for preheating the working fluid operating the binary power cycle.
Binary cycle systems are reviewed by V. K. Johnson et al., in a 1969 publication Timarit VFI, entitled "Optimisation of Geothermal Power Plant by use of Freon Vapour Cycle" which describes a number of arrangements for using geothermal fluid composed of a mixture of brine and steam. Scheme 4 proposed in this article discloses separating the steam from the brine, and then passing the steam directly to a steam turbine. The steam exhausted from this turbine condenses at a slight vacuum in a Freon cooled steam condenser. The brine passes directly to a first heat exchanger which heats the Freon from the steam condenser before the heated Freon is passed to a Freon turbine. The Freon exhausted from this turbine is condensed using ambient cooling water. The spent brine from the first heat exchanger is combined with the steam condensate from the steam condenser to furnish a mixture that passes through a second heat exchanger for preheating the condensed Freon before it is recirculated by supplying it to the steam condenser. The cooled mixture from the second heat exchanger is then disposed of.
Although the steam condenser in scheme 4 operates at a slight vacuum, and the arrangement of the heat exchangers enables relatively efficient use of the available heat, the actual overall efficiency of this scheme is not high because the brine in not used efficiently. It is an object of the present invention, therefore, to provide a new and improved apparatus and method for using the same in which the overall efficiency will be relatively high due to the efficient use of the relatively high temperature steam and brine present in the geothermal fluid.